Improve shortcut keys on the sidebar.
Pressing once the specified shortcut key will display the sidebar app, and pressing it again will minimize and return it to the sidebar. It will be easier to navigate if that was implemented.
Example:
Let Ctrl+Shift+1 = Messenger;

1. User presses Ctrl+Shift+1, Messenger shows.
2. User pressed Ctrl+Shift+1 again, Messenger hides.

.
Also, allow us to organize the sidebar apps by just clicking and holding the sidebar app icon until it triggers some kind of event that will allow us to reposition it by dragging it to another position. It is similar to Discord's way of organizing the servers you have joined. Dragging them to places to reorganize.
Example:

1. Click and hold the Messenger icon, then drag it wherever in the sidebar.

@leocg Thank you for your reply! But isn't it a bit of a hassle? I couldn't even remove Yahoo! from the y. I tried setting YouTube to asd and it doesn't work.

And it seems that I need to search for each and every site's "Query URL" to make it work.

Also, why should a user bother adding them manually when most of the website already done all the work to facilitate users' use.

And as I mentioned in my OP, Opera is a chromium-based browser too, why it is not being implemented? Is there any reason?

Don't get me wrong, I like using Opera. It could play 4k 60fps videos smoothly compared to other chromium-based browsers which stutter horribly. It's just doesn't feel right because it’s missing a feature that all the same chromium-based browsers have long had.

Allow users to type on the Omnibox/address bar a website and the Omnibox will suggest pressing Tab to Search to directly search without loading the whole website.

I've been keeping suggesting it for a long time ago now. Whenever there's an update, I hope that it would have been implemented, but still not.

I was a chrome user since it was launched, and if my memory serves me right, I believe I've been using the Tab to Search feature since 2016. I just switched from chrome to try other chromium-based browsers since it uses too many resources.

I don't know why it's not implemented in Opera when it's a chromium-based browser. All other chromium-based browsers have it for years already, why doesn't Opera?

This is a very useful feature. It saved me a lot of time. Rather than loading the whole e.g. Youtube.com, I'll just type YouT, press TAB then type what would I like to search, and ENTER!